1. Field of the Invention
The present invention relates to the metering of energy consumption and more particularly to the metering of energy consumption using acoustic signals.
2. Background Information
For many communities around the world, the delivery of heat to buildings is done via the mass transfer of heated water. The water is heated at a central location, such as a co-generating electric power plant, and delivered to individual residences, apartment buildings, and places of business via a complex network of water pipes. Wherein each residence, apartment building, or place of business may have numerous stations such as radiators to which the heated water is delivered, metering of consumption typically occurs, if at all, only at the inlet for the building or location.
When the building receiving the heat is an apartment building, each heating station may be "owned" by a particular user or resident, and the actual amount of usage for each user may vary. Because individual usage is not determined, the average cost for heat is apportioned to residents of the apartment building, regardless of individual usage. For situations in which the building is not metered, apportioning of the cost may extend across all buildings served by a central generating plant. In economics, this type of cost sharing is known as "average cost pricing." A consequence of average cost pricing is that the individual user has little or no economic incentive to conserve heat because the individual user cannot appreciably affect the cost of his individual heating bill through conservation. This lack of incentive to conserve energy leads to wasted energy, and the related excess fuel consumption results in many environmental harms.
The amount of energy consumed by a particular station of a mass transfer heat delivery system over a given period time can be determined as a function of 1) the temperature differential between the input and the output of the station, 2) the cross-sectional area of the inlet pipe into the station, and 3) the flow rate of heated water through the pipe. The mathematical relationship is given by the following equation: EQU Q=cAV.sub.f .DELTA.Tw,
wherein Q is the heat transferred, c is the specific heat of water, A is the cross-sectional area of the inlet pipe, V.sub.f is the velocity of flow, and .DELTA.T.sub.w is the temperature differential of the water at the input and outputs of the station. Wherein a liquid or gas other than water is used, the specific heat of that liquid or gas is substituted for the specific heat of water.
The cross-sectional area of the inlet pipe and the flow rate of heated water through the inlet pipe define the volume of heated water that passes through the station during the given period of time, and the temperature differential may be used to calculate the amount of energy transfer once the volume of the water is known.
Assuming that the cross-sectional area of the inlet pipe is fixed and known, all that remains is to determine both the temperature differential and the flow rate for the given period of time. Once determined, the temperature differential and the flow rate can be used to calculate the amount of heat consumed by the station during the given period of time. If the period of time is a fixed interval and the energy consumed over time by a station is continually monitored, the individual user may be incrementally charged for his energy consumption. This leads to a shift from "average cost pricing" to "marginal cost pricing," in which the individual user has an economic incentive to conserve energy, as conservation efforts have a direct and immediate effect on the amount the individual user pays for energy. "Marginal cost pricing" is also known as "incremental costing."
There are prior art systems that use acoustic signals to measure the rate of flow of a liquid through large diameter pipes. Such systems are useful, for example, for determining the flow rate through oil pipelines. Such systems are typically non-invasive, i.e. the systems are attached to an existing pipe without breaching the wall of the pipe. Acoustic signals are transmitted through the outer wall of the pipe by a first transducer and received at the outer wall of another portion of the pipe by a second transducer. The Doppler shift of the acoustic signal bouncing off particulates in the fluid or shifts in transit time are used to measure flow rates. The diameter of oil pipelines and the like are quite large, and attempts to modify prior non-invasive systems to measure flow rates in small diameter pipes such as those used for radiators have resulted in limited success. In heating applications, scale deposited on pipe walls typically thwarts measurement using prior art non-invasive systems.